On most of the fifth wheels in use today, tractor and semi-trailer are joined together by flexible supply lines, by which an electrical and pneumatic supply is realized for the semi-trailer. What is more, it is also possible to provide control signals or a hydraulic supply of the semi-trailer by appropriate supply lines. The coupling of the supply lines is done by hand, in that a plug-in element located on the supply line is inserted at the first supply console. Before uncoupling the semi-trailer, the supply lines are separated and the loose plug-in elements are usually hung on parking plug strips arranged on the tractor and secured here for driving without a semi-trailer. Such a prior art is disclosed by GB 2 204 844 A.
Meanwhile, in order to reduce the operating expenses, automated line coupling systems have become known, corresponding to DE 101 55 056 A1, and they have also come to be used to a significant degree. Such a system can comprise, for example, a plug-in wedge engaging with the center pin of the semi-trailer, which is introduced into the entry opening of the fifth wheel during the coupling operation. After this, a laterally movable jack connection is inserted into the plug-in wedge by motorized operation to bring about a contacting. In other systems, stationary mounted plug and socket come together by the coupling process of tractor and semi-trailer.
It would be possible to entirely replace with these new automated line coupling systems the original, manually operated systems with one or more supply lines and a plug-in element located on each one of them, being connected to the first supply console. But this would require, for reasons of compatibility, that all tractors and semi-trailers of a fleet of trucks be fully retrofitted with automated line coupling systems. Otherwise, in mixed truck parks, it might happen that an already retrofitted tractor, for example, cannot supply power and control signals to a conventional semi-trailer.